Halogen filament lamp having an internal all protection arrangement

ABSTRACT

A halogen filament lamp having two pinch seals in which at least one of the seals a rod is embedded. The rod, which is secured at one end to a sealing foil and at the other end to the axially stretched filament, provides an improved internal fuse for the lamp.

United States Patent [191 TJampens et al.

Jan. 9, 1973 [58] Field of Search ..3l3/222, 315, 333, 223, 331, 3l3/332,3l7, 3l8;3l5/73 [56] References Cited [75] Inventors: Germain Remi TJampens; Victor Rosallie Notelteirs; Eduard Jozef UNITED STATES PATENTS Philomena Janssen, all of Emmasin- 3,470,4l0 9/1969 Patsch ..3l3/3l5 X Netherlmds 3,448,322 6/1969 Millikan et al. ..3l3/3l8 [73] Assignee: U.S. Philips Corporation, New

York, NY. Primary Examiner-Alfred L. Brody Filed: Feb. 1970 Attorney-Frank R. Tnfan [21] Appl. No.: 12,693 [57] ABSTRACT A halogen filament lamp having two pinch seals in [30] Forei n Appli tion Pri it D m which at least one of the seals a rod is embedded. The rod, which is secured at one end to a sealing foil and Feb. 21, 7 Netherlands at t t etched p o vides an improved internal fuse for the lamp. [52] U.S. Cl. ..313/222, 313/317, 313/331 [51] Int. Cl "H011 5/50, HOlk 1/18 5 Claims, 2 Drawing Figures Hllit fannin HALOGEN FILAMENT LAMP HAVING AN INTERNAL ALL PROTECTION ARRANGEMENT The invention relates to an electric filament lamp, particularly a halogen filament lamp, which is formed as a lamp vessel closed by two pinch seals, such lamp has at least one of the ends of the coiled-coil filament stretched in said lamp vessel secured in one of the pinch seals to a rod which is partly inserted in the end. The filament with its rod portion projecting from the end, is secured to a foil incorporated in the pinch seal. The foil is connected to a current conductor projecting from said pinch part outside the lamp. Such a halogen filament lamp is known as a double-pinch lamp.

The filament lamp is constructed with a coiled-coil filament which is meant as a compact light source. This type of electric filament lamp, which has a high efficiency suitable inter alia for photographic purposes, comprises an internal protective arrangement to prevent the switched-on lamp from exploding at the end of the life of the lamp. More particularly, at the end of lamp life at which time the filament is interrupted a discharge lamp is actually formed in which an arc is maintained. The lamp then operates as an arc lamp with a current strength which is so large that the lamp seals and even the connections of the lamp housing can melt.

To avoid such effect, in the known filament lamps one of the ends of the coiled coil filament is stretched and incorporated in the other pinch seal together with a molybdenum foil. It has been found in practice that this results in a non-negligible lamp weakening. Moreover the drawback of said construction is that just in the case of the coiled coil filament a particularly large temperature gradient occurs at that place where the rod ends in the coil so that at that place also the lamp is weakened.

The present invention is based on the recognition of the fact that a protective operation can be obtained which is at least as effective as in the known halogen filament lamp, if that side of the pinch where the above-mentioned rod is already sealed in has a slightly different construction.

For that purpose the invention is characterized in that the rod is entirely embedded in the pinch seal.

Since the rod is entirely incorporated in the pinch seal, the advantage obtained is that no large temperature gradients occur as described above, and no arc can form. Since as a result of this construction, it is no longer necessary to expandone of the ends of the filament to form a fuse, it is now possible to secure the filament at either end to a rod and to embed the rods entirely in the associated pinchseals. This results in a very rigid lamp construction which may comprise a double arc protection arrangement if desired. Such arrangement insures that both ends of the lamp operate in the protective manner described.

It has been found experimentally that a particularly good protective operation can be obtained if the shortest distance in the material of the pinch seal between a rod and the internal space of the lamp vessel is at least one millimeter.

In order that the invention may be readily carried into effect, one embodiment thereof will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which FIG. 1 shows a halogen filament lamp of the known type and FIG. 2 shows the halogen lamp according to the invention.

FIG. 1 shows a known halogen filament lamp which comprises a tubular envelope 1 of glass and which has flat pinch seals 3 and 5, respectively, at either end. A so-called coiled coil filament 7 of tungsten wire is stretched out in said lamp which filament has a particularly short length and which extends axially in the tubular envelope 1. The coiled coil filament 7 shown has a comparatively short length. The halogen filament lamp shown comprises a molybdenum foil portion 9 and a tungsten or molybdenum rod 11 secured to said foil and formed as a mandril around which one of the ends of the coiled coil filament 7 is wound. A rod may serve as a mandril which comprises a helical groove. For this purpose, a rod is usually chosen around which a wire is helically wound. The assembly can then be screwed in one end of the filament in such manner that a rigid connection is obtained. Furthermore a current conductor 13 is secured to the foil 9. The foil 9, the rod 11 and the current conductor 13 are incorporated in the pinch seal 3 in the manner shown. The other end of the coiled coil filament 7 is expanded and incorporated in the pinch seal 5 and secured at its end to the foil 15 to which finally the output conductor 17 is secured. In this known lamp, the end of the filament 7 facing the pinch seal 5 is constructed as a fuse within the envelope 1, by means of which fuse the lamp seals and the external circuit are protected from damage by strong currents in extraordinary circumstances occurring When the lamp filament is interrupted.

The lamp according to the invention shown in FIG. 2 in general has the same shape as that shown in FIG. 1. In this case also a rod 19 is present which is surrounded at one end by a few turns of the filament 21 and is secured to the foil 23 incorporated in the pinch seal 25 with its end remote from said filament. In this embodiment, however the whole rod 19 is embedded in the pinch seal 25 in such manner that there is some distance between the inner space 27 of the lamp. The advantage of incorporating the rod 19 entirely in the pinch seal 25 is that, at the junction between the end of the rod 19 and the filament 21, the large temperature gradient which is present in the corresponding junction in the construction shown in FIG. 1 is hardly noticeable. Actually this rod is entirely incorporated in the pinch seal 25 in which an efficient heat dissipation takes place in the glass mass. It has been found that an internal lamp arc protection arrangement can be obtained by embedding the rod 19 entirely in the pinch seal. It has been found experimentally that the distance a for lamps operating above 24 volt should be at least 1 millimeter per centimeter of filament if it is to be an excellent arc protection arrangement the quality of which is at least comparable to that of the lamp shown in FIG. 1 in which the expanded part of the filament 7 incorporated in the other pinch seal serves as a fuse.

What has been described above for the pinch seal 25 can likewise be applied to the other pinch seal 29 in which a beam 31 constructed as a mandril is also embedded entirely in the seal.

What is claimed is:

' 1. An electric filament lamp comprising an envelope having at least one pinch seal, anh'alogen atmosphere within said envelope, a current conductor including a metal foil portion embedded within said pinch seal, a

coiled coil filament within said envelope, and internal arc protection means comprising a rod entirely embedded within said pinch seal, said rod being independent of said conductor and filament, one end of said rod being connected to said metal foil portion of said current conductor and the other end being secured by means to an end of said coiled filament at a point within said pinch seal.

2. An electric filament lamp comprising an envelope having pinch seals at the ends, an halogen atmosphere within said envelope, current conductors including metal foil portions embedded within said pinch seals, a coiled coil filament within said envelope and internal arc protection means comprising rods entirely embedded within said pinch seals and spaced from the inner walls of the envelope containing said halogen atmosphere, the ends of said rods remote from said filament being connected to said metal foil portions of said current conductors and the other ends of said rods being secured by means to the ends of said filament at points within said pinch seals.

3. An electric filament lamp as claimed in claim 2 wherein said point within said pinch seal is at a distance from the inner wall of the envelope containing said halogen atmosphere that is at least I millimeter per centimeter of filament.

4. In a halogen-type filament lamp of the type having at least one pinch seal, a coiled coil filament and current carrying means wherein the improvement comprises internal arc protection means including: a rod entirely embedded within said pinch seal, said rod being independent of said current carrying means and filament, one end of said rod being connected by means to said filament within said pinch seal, the other end of said rod being connected to said current carrying means.

5. The lamp as claimed in claim 4 wherein the distance of the rod end which is connected to said filament is at least 1 millimeter per centimeter of filament as measured from the internal end of said pinch seal. 

1. An electric filament lamp comprising an envelope having at least one pinch seal, an halogen atmosphere within said envelope, a current conductor including a metal foil portion embedded within said pinch seal, a coiled coil filament within said envelope, and internal arc protection means comprising a rod entirely embedded within said pinch seal, said rod being independent of said conductor and filament, one end of said rod being connectEd to said metal foil portion of said current conductor and the other end being secured by means to an end of said coiled filament at a point within said pinch seal.
 2. An electric filament lamp comprising an envelope having pinch seals at the ends, an halogen atmosphere within said envelope, current conductors including metal foil portions embedded within said pinch seals, a coiled coil filament within said envelope and internal arc protection means comprising rods entirely embedded within said pinch seals and spaced from the inner walls of the envelope containing said halogen atmosphere, the ends of said rods remote from said filament being connected to said metal foil portions of said current conductors and the other ends of said rods being secured by means to the ends of said filament at points within said pinch seals.
 3. An electric filament lamp as claimed in claim 2 wherein said point within said pinch seal is at a distance from the inner wall of the envelope containing said halogen atmosphere that is at least 1 millimeter per centimeter of filament.
 4. In a halogen-type filament lamp of the type having at least one pinch seal, a coiled coil filament and current carrying means wherein the improvement comprises internal arc protection means including: a rod entirely embedded within said pinch seal, said rod being independent of said current carrying means and filament, one end of said rod being connected by means to said filament within said pinch seal, the other end of said rod being connected to said current carrying means.
 5. The lamp as claimed in claim 4 wherein the distance of the rod end which is connected to said filament is at least 1 millimeter per centimeter of filament as measured from the internal end of said pinch seal. 